The aim of this project is a molecular description of the DNA sequence and DNA-protein interactions that comprise the pericentric heterochromatin in Drosophila melanogaster. An understanding of the structure of condensed heterochromatin will give insight into the molecular mechanism of other homologous chromosome associations such as meiotic pairing, ectopic pairing, polytene chromosome formation as well as chromocenter aggregation. We will focus on the 1.688 g/cu. cm satellite of D. melanogaster. We will determine the repeating sequence of this satellite and homologous satellites from other closely related species in order to understand the evolutionary history of this chromosomal region. We will search for proteins that associate specifically with those sequences by using a nitrocellulose filter binding assay. We will also study the interaction between any such specific nonhistone proteins and histones. By understanding the interaction between histones, nonhistones and repeated DNA sequences, we hope to understand the forces which condense heterochromatin.